1. Field of the Invention
This invention relates to a toner used in electrophotography, electrostatic recording, toner jet recording and the like, and a process cartridge making use of the toner.
2. Related Background Art
Conventionally, as resins for toners, vinyl copolymers (such as styrene resins) and polyester resins are chiefly used. The vinyl copolymers such as styrene resins show superior pulverizability when toners are produced, and have superior high-temperature anti-offset properties because they can be made to have high molecular weight with ease. However, in an attempt to lower molecular weight in order to improve low-temperature fixing performance, anti-blocking properties and developing performance may come poor. As for the polyester resins, though having high glass transition temperatures, they can readily provide resins having low softening points, and, when melted by heating, have so good wettability to fixing sheets such as paper that the fixing can sufficiently be performed at lower temperatures.
On the other hand, however, the polyester resins simultaneously have a disadvantage that they tend to cause a phenomenon of high-temperature offset. For the purpose of providing resistance to such offset, a large number of proposals have been made, e.g., on making molecular weight distribution double-peak, on a polyester resin containing chloroform-insoluble matter as disclosed in Japanese Patent Publication No. 63-60904, and on a polyester resin having THF-insoluble matter as disclosed in Japanese Patent Application Laid-open Nos. 3-269542 and No. 4-70765.
Using as binders the polyester resins having such insoluble matter may make it possible to obtain toners having superior anti-offset properties, but may cause the polyester resins, which have a problem in improving pulverizability because of their original toughness, to have much poorer pulverizability. This may lower productivity greatly in producing small-particle-diameter toners which are necessary for achieving higher image quality of copied images. Also, because of their relatively high softening points, it can not necessarily be said to promise good low-temperature fixing performance. Further, as disclosed in Japanese Patent Application Laid-open Nos. 3-197971 and 8-297378, the molecular weight of insoluble matter is specified in addition to the molecular weight of soluble matter, but, under the existing circumstances, it is sought to make further improvement from the viewpoint of high-temperature anti-offset properties.
Furthermore, as disclosed in Japanese Patent Application Laid-open No. 2000-029246, the dielectric dissipation factor (tan δ) of polyester resin is specified in order to improve low-temperature fixing performance and high-temperature anti-offset properties. However, the dielectric dissipation factor of toner is not measured, and hence it can not be said to have sufficiently controlled the performance of toner. Any annealing is also not carried out when the polyester resin is taken out of a reaction chamber, and hence, in order to achieve the desired quantity of THF-insoluble matter, it is necessary to set conditions under which the reaction may more proceed or to use a cross-linking agent in a larger quantity. However, the THF-insoluble matter formed under such conditions tends to come hard, so that not only the low-temperature fixing performance may not sufficiently be satisfied, but also the pulverizability in producing the toner may come poor, resulting in a very low productivity of the toner.
Thus, although there are disclosures as to the quantity of insoluble matter and the molecular weight distribution of soluble matter, there is no disclosure which refers to any strict control of insoluble matter in respect to different solvents. Also, under the existing conditions, those which can highly satisfy all the low-temperature fixing performance, high-temperature anti-offset properties and toner productivity have not yet been available.